Transversely-excited film bulk acoustic resonator using pre-formed cavities

1. An acoustic resonator device comprising:

a substrate comprising a cavity and an alignment pattern in a surface of the substrate, wherein the cavity and the alignment pattern have a same depth;

a piezoelectric plate having front and back surfaces, the back surface attached to the surface of the substrate, wherein a portion of the piezoelectric plate that spans the cavity forms a diaphragm; and

an interdigital transducer (IDT) on the piezoelectric plate, wherein interleaved fingers of the IDT are on the diaphragm.

2. The device of claim 1 , wherein the IDT and the piezoelectric plate are configured such that a radio frequency signal applied to the IDT excites a primary acoustic mode in the diaphragm.

3. The device of claim 1 , wherein the alignment pattern is a trench.

4. The device of claim 1 , wherein the alignment pattern is configured to facilitate alignment of the piezoelectric plate and the interleaved fingers.

5. The device of claim 1 , wherein the substrate comprises Si.

6. The device of claim 5 , wherein the substrate further comprises an SiO 2 coating.

7. The device of claim 1 further comprising at least one of a front-side dielectric layer on the front surface of the piezoelectric plate and a back-side dielectric layer on the back surface of the piezoelectric plate.

8. A filter device comprising:

a substrate comprising a plurality of cavities and an alignment pattern in a surface of the substrate, wherein the plurality of cavities and the alignment pattern have a same depth;

a piezoelectric plate having front and back surfaces, the back surface attached to the surface of the substrate, wherein portions of the piezoelectric plate that span each of the plurality of cavities form respective diaphragms; and

a conductor pattern on the piezoelectric plate, the conductor pattern comprising a plurality of interdigital transducers (IDTs) of a respective plurality of acoustic resonators, wherein interleaved fingers of each of the plurality of IDTs are on respective diaphragms.

9. The device of claim 8 , wherein each of the plurality of IDTs and the piezoelectric plate are configured such that radio frequency signals applied to respective IDTs excite primary acoustic modes in the respective diaphragms.

10. The device of claim 8 , wherein the alignment pattern is a trench.

11. The device of claim 8 , wherein the alignment pattern is configured to facilitate alignment of the piezoelectric plate and the interleaved fingers.

12. The device of claim 8 , wherein the substrate comprises Si.

13. The device of claim 12 , wherein the substrate further comprises an SiO 2 coating.

14. The device of claim 8 further comprising at least one of a front-side dielectric layer on the front surface of the piezoelectric plate and a back-side dielectric layer on the back surface of the piezoelectric plate.

15. A method of forming an acoustic resonator device, the method comprising:

forming a cavity and an alignment pattern in a substrate, wherein the cavity and the alignment pattern have a same depth;

attaching a back surface of a piezoelectric plate having front and back surfaces to the surface of the substrate, wherein a portion of the piezoelectric plate that spans the cavity forms a diaphragm; and

forming an interdigital transducer (IDT) formed on the piezoelectric plate, wherein interleaved fingers of the IDT are on the diaphragm.

16. The method of claim 15 , wherein the IDT and the piezoelectric plate are configured such that a radio frequency signal applied to the IDT excites a primary acoustic mode in the diaphragm.

17. The method of claim 15 , wherein the alignment pattern is a trench.

18. The method of claim 15 , wherein the alignment pattern is configured to facilitate alignment of the piezoelectric plate and the interleaved fingers.

19. The method of claim 15 , wherein the substrate comprises Si.

20. The method of claim 19 , wherein the substrate further comprises an SiO 2 coating.